(1) Field of the Invention
The invention relates to a light source module, and more particularly to a backlight module.
(2) Description of the Related Art
FIG. 1 is a schematic view showing the structure of a conventional backlight module 100. As shown in FIG. 1, the conventional backlight module 100 includes a cold cathode fluorescent lamp (CCFL) 110, a light guide plate 120, a reflection sheet 130, a reverse prism sheet 140, and a diffusion sheet 150. The CCFL 110 is capable of emitting a light beam 112. The light beam 112 enters into the light guide plate 120 through a light incident surface 122 of the light guide plate 120, and is reflected to a light emitting surface 124 of the light guide plate 120 by the reflection sheet 130. The light beam 112 emits outside of the light guide plate 120 through the light emitting surface 124 and transmits to the reverse prism sheet 140.
The reverse prism sheet 140 is composed of a light transmissive substrate 142 and a plurality of reverse prism rods 144. Generally, the light beam 112 (e.g. partial light beam 112b) emitted from the light emitting surface 124 of the light guide plate 120 at an angle in a range between 65 degrees and 75 degrees emits towards the light transmissive substrate 142 through the reverse prism sheet 140, and then exits by a light emitting surface 142a of the light transmissive substrate 142 at an angle in a range between −20 degrees and 20 degrees for emitting to the diffusion sheet 150 to form a plane light source with a small light emitting angle. In addition, the light beam 112 (e.g. partial light beam 112a) emitted from the light emitting surface 124 of the light guide plate 120 at an angle out of a range between 65 degrees and 75 degrees may exit by the light emitting surface 142a of the light transmissive substrate 140 at an angle out of a range between −20 degrees and 20 degrees, and the light beam 112 (e.g. partial light beam 112a) may not be used.
FIG. 2 is a distribution diagram of brightness to light emitting angle of the reverse prism sheet according to FIG. 1. As shown in FIG. 2, 63% of the light beam 112 (the light beam 112 in a area 2 shown in the diagram) transmits through the reverse prism sheet 140 and exits in a approximately perpendicular emitting angle (in a range between −20 degrees and 20 degrees) to form a plane light source, and 37% of the light beam 112 (the light beam 112 in a area 1 and a area 3 shown in the diagram) may not be used so that the light efficiency of the backlight module 100 is hard to be increased.
Referring to FIG. 1, in order to prevent the shape of the reverse prism rods 144 from being seen by viewers and avoid the moiré or the Newton rings when the liquid crystal plate is arranged on the backlight module 100, the diffusion sheet 150 is arranged on the reverse prism sheet 140 to blur the shape of the reverse prism 144. At the same time, the diffusion sheet 150 may also cause the light loss and decrease the efficiency of the backlight module 100.